1. Field of the Invention
The present invention relates to a waveguide-microstrip line converter for transmitting signals transmitted through a waveguide packet with a dielectric to a microstrip line without signal transmission loss.
2. Description of the Prior Art
In microwave transmission systems, a waveguide and a microstrip line are employed in a transmission circuit. Accordingly, signals are often required to be transmitted from the waveguide to the microstrip line (in some cases, the reverse). Since the dominant mode of a general rectangular waveguide is TE mode while the mode of a microstrip liner is TEM mode, the waveguide and the microstrip line need to be connected through a mode converter for impedance matching.
A conventional waveguide-microstrip line converter is shown in FIG. 4, in which there are shown a short-circuit waveguide 21, a probe 22, a MIC substrate 23, a microstrip line 24, solder 25, a mount 26, screws 27, and a recess 28 formed in one wall of the short-circuit waveguide 21.
The metallic short-circuit waveguide 21 is hollow. The probe 22 is provided inside the metallic short-circuit waveguide 21 and is fixed at one end thereof to the short-circuit waveguide 21 with the screws 27 so that the other end thereof projects through the recess 28 outside the short-circuit waveguide 21. The probe 22 is soldered at the free end of the portion projecting from the short-circuit waveguide 21 by the solder 25 to the microstrip line 25 formed on the MIC substrate 23. The MIC substrate 23 and the short-circuit waveguide 21 are attached to the mount 26 to constitute a waveguide-microstrip line converter.
However, several problems have been encountered by the prior art waveguide-microstrip converter. One of the problems is that, since the probe 22 is fastened with the screws 27 to the surface of the short-circuit waveguide 21 carrying large surface current and the probe 22 is liable to be in incomplete contact with the short-circuit waveguide 21, the high frequency resistance across the joint of the probe 22 and the short-circuit waveguide 21 is large, and thereby signal transmission loss is increased. Another problem is that the screws 27 are liable to be loosened by vibration and hence the probe 22 is liable to be loosened, which also increases signal transmission loss.